Dot matrix printers, in particular because of the limited available travel of their print wires, as well as certain other types of printers, must have their head assembly closely spaced from the surface of the paper upon which their wires print through the interposed ribbon. In order to accommodate multiple sheets of paper when multiple copies are desired, it is necessary that the print head be adjustable in a direction toward and away from the surface upon which the paper is supported during printing to vary the spacing therebetween. It is also desirable that the print head be retractable away from the support surface to facilitate paper and ribbon changing. Heretofore such adjustment has generally been accomplished by slideably mounting the print head on its carriage, which makes adjustment difficult when the printer is operating.
In another aspect of dot matrix printers, it may be desirable to displace the dot matrix printer wire array in a vertical direction into one of two or more discrete positions to effectively at least double the number of dot positions available for printing from the print head wire array, for example, to produce a more readable pattern by overlapping the printed dots, or to make possible the use of fewer print wires. The latter is suggested, for example, in U.S. Pat. Nos. 3,757,346 and 3,759,359, both of which disclose print head carriage mounted mechanisms for accomplishing the result.